Post on 17-Dec-2015
RNA interference improves motor and neuropathologival abnormaliies in a Huntinton’s
disease mouse model
Jenna KausnerPBIO 427
5/13/11
Huntinton’s disease
Dominant neurodegenerative disease
Polyglutamine repeat expansions (CAG, codon, Q) in exon 1 of huntingtin gene (htt). Usually >35 CAG repeats.
Toxic gain of function mutation causing gradually damage to certain areas in brain
Symptoms
Behavioral and cognitive disturbances
Involuntary movements (chorea)
Neuronal inclusions
Striatal and cortical neurodegeneration
Huntingtin Protein (htt) Expressed in all mammalian cells,
highest in brain and testes
Function not entirely clear in humans
Interacts with proteins involved in transcription, cell signaling, and intracellular transporting
Huntington Protein (htt)
Glutamine is polar and causes interactions with other proteins when overproduced in htt
Then, htt forms H-bonds with each other, resulting in a protein aggregate instead of normal folding protein.
Aggregates over time result in neuronal inclusions.
Hypothesis By directly inhibiting the expression of
mutant htt, HD associated symptoms may be reduced or prevented.
This study tested if RNAi induced by short hairpin RNAs (shRNAs) could improve HD-associated abnormalities by reducing expression of mutant htt in a transgenic HD mouse model.
Plasmids
HD-N171-82Q gene expressed from the pCMV-HD-N171-82G plasmid.
HD-N171-82Q is a truncated htt fragment
shRNAs and U6 promoter were amplified with PCR to target human htt (shHD2.1), eGFP (shGFP) or E. coli β-galactosidase (shLacZ).
Adenoassociated Virus Constuction
PCR products were cloned, sequenced, and inserted into adenoassociated virus (AAV) plasmid pAAV.CMV.hrGRP with AAV serotype 2 inverted terminal repeats, CMV-humanized Renilla GFP (hrGFP)-simian virus 40 poly(A) reporter cassette.
Htt expression in Vitro HEK293 cells were transfected with
pCMV-HD-N171-82G and plasmid expressing shHD2.1, shGFP, or shLacZ.
RNA was isolated 48 hours after transfection and Northern blot analysis performed with human htt probes or human GAPDH probes as a control.
Htt expression in Vitro HEK293 transfected cells were lysed to
recover total protein and Western blot analysis was performed with actin as a control.
Expression of shRNA in mouse brain
Mice were injected with AAV plasmids containing U6-driven shHD2.1 or shLacZ at four-weeks old and analyzed at four-months.
After injection into mouse striatum, shHD2.1 expression was analyzed by isolating total RNA from grGFP-positive striata using Northern blot analysis.
AAV.shHD2.1 reduces HD-N171-82Q expression in Vivo
To test the effect of RNAi on neuronal inclusions associated with HD, tissues were harvested from mice at about 5.5 months old and RNA was isolated.
In striata from mice injected with AAV.shHD2.1, htt-reactive inclusions were absent and mutant htt expression was reduced.
Immunofluorescence
Coronal sections were isolated from mice and stained with mEM48 antibody followed by goat anti-mouse secondary antibody
Images were captured using fluorescent microscopy
Behavioral analysis
Stride length measurements were taken by injected mice walking across a paper-lined chamber and into an enclosed box and measuring footprint tracings.
There was a noticable weight difference between HD-N171-82Q and wild type mice that was not normalized by RNAi directly to the striatum.
Rotarod performance test
Mice were injected at 4 weeks of age and tested at 10 and 18 weeks old.
Amount of time it took mice to fall was measured.
Conclusion Motor and neuropathological
abnormalities in a HD mouse model are significantly improved using AAV delivered shRNA to reduce striatal expression of pathogenic htt allele.
Suggests feasibility of treating HD with direct reduction of mutant htt gene expression using RNAi.